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Saturday, May 16, 2015

Plants convert
carbon dioxide from the atmosphere into organic carbon via
photosynthesis. Most of this carbon eventually returns to the atmosphere
when plant material (or animals that eat plants) decompose. A small
fraction of this material, however, ends up in rivers. They carry it out
to sea, where some settles to the seafloor and is buried and
disconnected from the atmosphere for millions of years and eventually
makes its way back to the surface in the form of rocks. At the same
time, rivers also erode carbon-containing rocks into particles carried
downstream. The process exposes carbon to air, oxidizing the previously
locked-up carbon into carbon dioxide that can leak back out to the
atmosphere.Credit: Illustration by Eric Taylor, Woods Hole Oceanographic Institution

Humans concerned about climate change are working to find ways of
capturing excess carbon dioxide (CO2) from the atmosphere and
sequestering it in the Earth. But Nature has its own methods for the
removal and long-term storage of carbon, including the world's river
systems, which transport decaying organic material and eroded rock from
land to the ocean.
While river transport of carbon to the ocean is not on a scale that will
bail humans out of our CO2 problem, we don't actually know how much
carbon the world's rivers routinely flush into the ocean -- an important
piece of the global carbon cycle.

But in a study published May 14 in the journal Nature, scientists from
Woods Hole Oceanographic Institution (WHOI) calculated the first direct
estimate of how much and in what form organic carbon is exported to the
ocean by rivers. The estimate will help modelers predict how the carbon
export from global rivers may shift as Earth's climate changes.

"The world's rivers act as Earth's circulatory system, flushing carbon
from land to the ocean and helping reduce the amount that returns to the
atmosphere in the form of heat-trapping carbon dioxide," said lead
author and geochemist Valier Galy. "Some of that carbon--'new'
carbon--is from decomposed plant and soil material that is washed into
the river and then out to sea. But some of it comes from carbon that has
long been stored in the environment in the form of rocks-- 'old'
carbon--that have been eroded by weather and the force of the river."

The scientists, who included Bernhard Peucker-Ehrenbrink, and Timothy
Eglinton (now at ETH Zürich), amassed data on sediments flowing out of
43 river systems all over the world, which cumulatively account for 20
percent of the total sediments discharged by rivers. The representative
rivers also encompassed a broad range of climates, vegetation,
geological conditions, and levels of disturbance by people.

From these river sediment flow measurements, the research team
calculated amounts of particles of carbon-containing plant and rock
debris that each river exported. They estimated that the world's rivers
annually transport 200 megatons (200 million tons) of carbon to the
ocean. The total equals about .02 percent of the total mass of carbon in
the atmosphere. That may not seem like a lot, but over 1000 to 10,000
years, it continues to add up to significant amounts of carbon (20 and
200 percent) extracted from the atmosphere.

Generally, plants convert CO2 from the atmosphere into organic carbon
via photosynthesis. But most of this carbon eventually returns to the
atmosphere when plant material (or animals that eat plants) decompose. A
small fraction of this material, however, ends up in rivers. They carry
it out to sea, where some settles to the seafloor and is buried and
disconnected from the atmosphere for millions of years and eventually
makes its way back to the surface in the form of rocks.

At the same time, rivers also erode carbon-containing rocks into
particles carried downstream. The process exposes carbon to air,
oxidizing the previously locked-up carbon into carbon dioxide that can
leak back out to the atmosphere. Until now, scientists had no way to
distinguish how much of the carbon whisked away by rivers comes from
either the biospheric or petrogenic (rock) sources. Without this
information, scientists' ability to model or quantitatively predict
carbon sequestration under different scenarios was limited.

To solve this dilemma, the scientists found a novel way to distinguish
for the first time the sources of that carbon--either from eroded rocks
or from decomposed plant and soil material. They analyzed the amounts of
carbon-14, a radioactive isotope, in the river particles. Carbon-14
decays away within about 60,000 years, so it is present only in material
that came from living things, and not rocks. Subtracting the portion of
particles that did not contain carbon-14, the scientists calculated the
percentage that was derived from the terrestrial biosphere: about 80
percent.

But even though biospheric carbon is the major source of carbon exported
by rivers, the scientists also discovered that rivers surrounded by
greater amounts of vegetation didn't necessarily transport more carbon
to the ocean. Instead, the export was "primarily controlled by the
capacity of rivers to mobilize and transport" particles. Erosion is the
key factor--the more erosion occurs along the river, the more carbon it
transfers to sea and sequesters from the air.

"The atmosphere is a small reservoir of carbon compared to rocks, soils,
the biosphere, and the ocean," the scientists wrote in Nature. "As
such, its size is sensitive to small imbalances in the exchange with and
between these larger reservoirs."

The new study gives scientists a firmer handle on measuring the
important, and heretofore elusive, role of global rivers in the
planetary carbon cycle and enhances their ability to predict how
riverine carbon export may shift as Earth's climate changes.

"This study will provide geochemical modelers with new insights on an
important link between the global carbon and water cycles," says Don
Rice, program director in the National Science Foundation's Division of
Ocean Sciences, a major funder of the research.

Research from Yale University shows that climate science literacy
is unrelated to public acceptance of human-caused global warming.

Deep public divisions over climate change are unrelated to
differences in how well ordinary citizens understand scientific evidence
on global warming, according to a new study published by Professor Dan
Kahan.

In fact, members of the public who score the highest on a
climate-science literacy test are the most politically polarized on
whether human activity is causing global temperatures to rise.

These were the principal findings of a Yale-led study published recently in the journal Advances in Political Psychology.
In the study, a nationally representative sample of 2,000 U.S. adults
completed a test measuring their knowledge of prevailing scientific
consensus on the causes and consequences of climate change. They also
indicated whether they believed that human activity is responsible for
global temperature increases in recent decades.

Consistent with national opinion surveys generally, the study found
that the American public is split on the existence of human-caused
climate change.

“The study participants were deeply divided along partisan lines,
with about 50% saying they do believe in human-caused climate change and
50% saying they don’t,” said Kahan, the Elizabeth K. Dollard Professor
of Law and Professor of Psychology at Yale Law School and the lead
researcher on the study.

Disagreement did not diminish, however, as the study subjects’
climate-literacy test scores increased. On the contrary, “those with the
highest scores were even more politically polarized,” Kahan said.

The climate-science literacy test consisted of questions derived from
reports issued by the U.N.’s Intergovernmental Panel on Climate Change
and by the U.S. National Oceanic and Atmospheric Administration and the
National Aeronautics and Space Administration.

“Generally speaking,” said Kahan, “both those who accept human-caused
climate change and those who don’t displayed very poor comprehension of
climate science.” For example, he said, most participants recognized
that carbon dioxide increases global temperatures, yet mistakenly
indicated that rising levels of atmospheric CO2 are expected to “reduce
photosynthesis in plants.”

“If you know carbon dioxide is a ‘greenhouse gas’ but think it kills
the things that live in greenhouses, then it’s safe to say you don’t
know much about climate science,” said Kahan.

Regardless of whether participants said they accepted that human
activity caused climate change, most recognized that scientists expect
climate change to create serious environmental dangers, including
increased coastal flooding. However, the vast majority of study
participants also associated global warming with risks wholly contrary
to scientific evidence, such as an increase in the incidence of skin
cancer.

Study participants who scored highest on a general-science-literacy
test did the best on the study’s climate-literacy test. But contrary to
the researchers’ expectations, those participants were not more likely
to agree on whether human activity is causing climate change, according
to the study.

Previous studies, Kahan said, have found the more science-literate
members of the public are more polarized. “Nevertheless, one might
reasonably have supposed that those individuals must at least differ in
their levels of climate-science literacy, maybe because of biased
interpretations of the evidence. But apparently that’s not what’s going
on,” said Kahan.

Kahan dismissed as “ridiculous” the suggestion that the study implies
there is no value in climate education. “We need even more research on
how to communicate climate science effectively, so people can make
informed individual and collective decisions,” he said.

Nevertheless, Kahan said the results justify reassessing at least
some popular common science-communication strategies. “One conclusion is
that it’s misguided to fixate on what percentage of the respondents in
an opinion survey say they ‘believe in’ climate change,” said Kahan.
“What people say they believe about global warming is not a measure of
how much they know, or even how worried they are about it; it is an
expression of their cultural identities.”

According to Kahan, the study also casts doubt on the value of
social-marketing campaigns that feature the message that “97% of climate
scientists” accept human-caused climate change.

“Republicans and Democrats alike already understand that climate
scientists have shown we face huge risks from global warming,” said
Kahan. “Just telling people that over and over — something advocacy
groups have been spending millions of dollars doing for over a decade —
misses the point: Positions on climate change have become symbols of
whose side you are on in a cultural conflict divorced from science.”

“That’s what has to change if as a society we are going to make use
of all we know about the dangers we face and how to abate them,” he
added.

Kahan pointed to the success of local political leaders in southeast
Florida in depoliticizing discussions of climate science, an example
that is discussed at length in the study.

The study was sponsored jointly by the Cultural Cognition Project at
Yale Law School, the Annenberg Public Policy Center of the University of
Pennsylvania, and the Skoll Global Threats Fund.

So what exactly is the intellectual laziness of Bill Maher
and Richard Dawkins? It is one of Illing’s several accusations leveled
at New Athiests, which I’ll summarize below:

1. New Atheists are just too stupid to realize that religion
isn’t about truths, but about fictions that make people feel good, and
structure their lives. Yes, Illing appears to be a
nonbeliever, and sees religion as promulgating untruths, but that
doesn’t matter, for those untruths give people meaning. This is a variant on the “Courtier’s Reply” trope, in which believers fault us for not tackling the Most Sophisticated Forms of Theology™
(the so-called “best arguments”). In this case, defenders of faith like
Illing simply admit that religious “truth claims” are all bogus, but
they don’t really care. In fact, the people who are at fault are not the
believers who structure their morality and behavior around those
bogus claims, but the atheists who take believers at their
word, apparently thinking erroneously that believers really believe.
That, says Illnig, is the fatal weakness of Maher and Dawkins (my
emphasis):

But there’s something missing in their critiques,
something fundamental. For all their eloquence, their arguments are
often banal. Regrettably, they’ve shown little interest in understanding
the religious compulsion. They talk incessantly about the untruth of
religion because they assume truth is what matters most to religious
people. And perhaps it does for many, but certainly not all – at least
not in the conventional sense of that term. Religious convictions, in
many cases, are held not because they’re true but because they’re
meaningful, because they’re personally transformative. New Atheists are
blind to this brand of belief.

It’s perfectly rational to reject faith as a matter of principle.
Many people (myself included) find no practical advantage in believing
things without evidence. But what about those who do? If a belief is
held because of its effects, not its truth content, why should its
falsity matter to the believer? Of course, most religious people
consider their beliefs true in some sense, but that’s to be expected:
the consolation derived from a belief is greater if its illusory origins
are concealed. The point is that such beliefs aren’t held because
they’re true as such; they’re accepted on faith because they’re
meaningful.

The problem is that the New Atheists think of God
only in epistemological terms. Consequently, they have nothing to say to
those who affirm God for existential reasons. New Atheist
writers tend to approach religion from the perspective of science: They
argue that a particular religion isn’t true or that the empirical claims
of religious texts are false. That’s easy to do. The more interesting
question is why religions endure in spite of being empirically untrue.
There are, of course, millions of fundamentalists for whom God is a
literal proposition. Their claims concerning God are empirical and
should be treated as such. For many [JAC: How many?
Most?], though, God is an existential impulse, a transcendent idea with
no referent in reality. This conception of God is untouched – and
untouchable – by positivist science; asking if God is true in this sense
is like asking how much the number 12 weighs – it’s nonsensical.

Now, really? How many religious people wouldn’t give a hoot if they
were told that what they believed was false? Would they say, “I don’t
care: I have existential reasons for believing in God.” As I wrote yesterday:

Sadly, the data show that while religion does have these
other functions, it’s simply not the case that truth is irrelevant. Even
theologians (the honest ones) admit that without an underpinning of
beliefs about what’s really true about the universe, religion
crumbles. Where would Christianity be if adherents thought that Jesus’s
divinity, crucifixion, and resurrection were just a fictitious but
convenient framework on which to hang their emotions? Would Mormons wear
their sacred underwear if theyknew Joseph Smith was really a
con man who fabricated those plates? Do the Sophisticated Critics really
believe that if Muslims knew for certain that Muhammed didn’t
get the Qur’an from the mouth of God, via an angel, but made it up
himself, that Islam would have the sway it does? Get serious.

I challenge Illing to stand on the steps of any mosque in Pakistan or
Iran and tell believers that it doesn’t matter whether what they think
about Muhammad or the inerrancy of the Qur’an is irrelevant; all that
matters is that the beliefs motivate their behavior. I suspect his
longevity would be severely reduced. And there are 1.6 billion Muslims
on this planet.

Note as well that Illing really does admit that believers must
undergird their behavior with acceptance of factual propositions, for he
says this:

“Of course, most religious people consider their beliefs
true in some sense, but that’s to be expected: the consolation derived
from a belief is greater if its illusory origins are concealed.”

I’m not sure what he means by “true in some sense”, but I suspect
that the 57% of Americans who think that Jesus was born of a virgin take
it as a real fact that Mary was not penetrated by a human male before
baby Jesus was born. And I think the 42% of Americans who think that
humans were created by God in their present form within the last 10,000
years are really thinking of actual years and an actual creator God.
(By the way, if the facts here aren’t all that important, why do
creationists keep trying to get this stuff taught in public schools?)

And what about this?:

The point is that such beliefs aren’t held because they’re true as such; they’re accepted on faith because they’re meaningful.

Illing has not thought this through. What is accepted on faith is
the religious epistemology: statements about the existence of God and
Jesus, Mohammed or Moroni, and the moral codes that stem from the
scriptures. They may not look at these propositions too closely, but
they believe them, and they undergird the faith of everyone except for
the highly rarefied and well-fed theologians who eschew the need for
truth.

But really, religion is not treated like fiction. Religious people
don’t act like all of scripture is fictional, nor do they act like they
don’t care whether scripture is fictional. At least some
truths matter. (For Christians, the one non-negotiable is the salvific
effect of Jesus’s death and resurrection.) You don’t see people basing
their lives and hopes and morality and meanings on things that are
palpably untrue, like the Harry Potter series or even The Brothers Karamazov. If you’re a normal person (i.e., not Karen Armstrong or David Bentley Hart), you must accept some fundamental truths about your faith if it’s to inspire you.

Hell, this is kindergarten stuff, realized even by theologians. I’ll give a few quotes, starting with the Bible itself:

But if there be no resurrection of the dead, then is Christ not risen:And if Christ be not risen, then is our preaching vain, and your faith is also vain.—Paul, 1 Cornithians 15:13-14

A religious tradition is indeed a way of life and not a set of
abstract ideas. But a way of life presupposes beliefs about the nature
of reality and cannot be sustained if those beliefs are no longer
credible.—Ian Barbour

I cannot regard theology as merely concerned with a collection of
stories which motivate an attitude toward life. It must have
its anchorage in the way things actually are, and the way they
happen.—John Polkinghorne

Likewise, religion in almost all of its manifestations is more
than just a collection of value judgments and moral directives. Religion
often makes claims about ‘the way things are.’ —Karl Giberson &
Francis Collins

That’s only a small sample; I have more for Illing if he wants them.
And here is what Americans actually believe to be true (percentage of
all Americans accepting the propositions below). This is not a small
minority of Americans—it’s MOST OF THEM:

A personal God concerned with you 68%Absolutely certain there is a God 54%
Jesus was the son of God 68%
Jesus was born of a virgin 57%
Jesus was resurrected 65%
Miracles 72%
Heaven 68%
Hell and Satan 58%
Angels 68%
Survival of soul after death 64%

2. Without the (false) verities of religion, people’s lives will lose meaning.

For [Dostoyevsky’s] part, God was a bridge to
self-transcendence, a way of linking the individual to a tradition and a
community. The truth of Christ was therefore less important than the
living faith made possible by belief in Christ. . .

“I’ve never seen anyone die for the ontological argument,” Camus
wrote, but “I see many people die because they judge that life is not
worth living. I see others getting killed for ideas or illusions that
give them a reason for living.” Today is no different; people continue
to kill and die in defense of beliefs that give their lives meaning and
shape.

. . . The New Atheists don’t have a satisfactory alternative for such
people. They argue that religion is false; that it’s divisive; that
it’s unethical; that it makes a virtue of self-deception; that it does
more harm than good – and maybe they’re right, but if they don’t
understand that, for many, meaning is more important than truth, they’ll
never appreciate the vitality of religion. To his credit, Sam Harris’
most recent book, “Waking Up,” grapples with these issues in truly
fascinating ways. Indeed, Harris writes insightfully about the necessity
of love, meaning and self-transcendence. But he’s a fringe voice in the
New Atheist community. Most are too busy disproving religion to
consider why it is so persistent, and why something beyond science will
have to take its place in a Godless world.

What we see here is the incredibly arrogant and condescending Little
People Argument: while rationalists like Illing can easily reject
religion’s truths and get along fine without them—he says, “It’s
perfectly rational to reject faith as a matter of principle. Many people
[myself included] find no practical advantage in believing things
without evidence”—the Little People can’t. They need their faith! I
guess the Little People who populate much of Northern Europe don’t
count.

Let us make one thing clear: it is a benefit to humanity to rid it of
false beliefs, even if you have nothing to put in their place. Many
people in the South structured their lives around the implicit
assumption that whites were far superior to blacks, and that a decent
society demanded the subjugation of blacks. Did the civil rights
movement offer something to replace the need of Southern whites
to feel superior? Nope; the movement simply rid society of a false and
invidious notion that people were inherently unequal and thus should be
treated unequally.

Likewise, New Atheists rid society of the belief that it’s being
monitored and tended by a celestial dictator. That alone is a good, for
it’s better to see the truth. I don’t see it as an inherent
responsibility of atheists to replace religion with something else that
gives people meaning, for I think that most people (as they have in
atheistic Europe) will find such meaning for themselves, and that it
will differ from person to person. I bet if you asked most Swedes how
they can possibly find meaning in their lives without religion, they’d
just look like you were crazy.

Which brings us to the last point:

3. New Atheists should be faulted for attacking religion without at the same time suggesting replacements for religion.

The New Atheists have an important role to play. Reason
needs its champions, too. And religion has to be resisted because there
are genuine societal costs. One can draw a straight line between
religious dogma and scientific obscurantism or moral stagnation, for
example. That’s a real problem. But if religion is ineradicable, we have
to find a way to limit its destructive consequences. Satire and
criticism are necessary, but they’re not sufficient.

People like Harris and the late Christopher Hitchens make a powerful
case for a more humanistic ethics. Harris writes admirably about the
need to be more attentive to the present, to the suffering of other
human beings. I agree. But if we want to encourage people to care about
the right things, we should spend as much time encouraging them to care
about the right things as we do criticizing their faith.

Here we see more arrogance—not from the New Atheists but from Illing.
Who is he to tell us how to spend our time? In fact, some of us
criticize religion, while others, like Phil Kitcher, Chris Stedman and
Alain de Botton—spend their time finding the substitutes for religion.
Isn’t that just as good as all of us spending our time doing both?

After all, we have the principle of comparative advantage at work:
let each of us do what he or she is good at. I am not good at suggesting
religion substitutes because I don’t believe that we need formal substitutes, and the evidence from modern Europe supports me. Nor do we have good studies to show a). what will count as a religion substitute for people, and b). whether people really need
those things to have a meaningful life. Since I think that religion is
on balance a harmful superstition, standing in the way of rational
discourse, and as a scientist who’s read theology I can do something
about that, that’s what I do. I’m not keen on finding religion
substitutes, and neither Illing nor I (nor anyone, I think) is
well qualified to tell people what can replace church. As water finds
its own level, so will people find their own meaning.

In the end, it’s not the New Atheists who are arrogant. How could we
be, if we’re wedded to rationality, doubt, and the use of evidence? Who
asks themselves more often questions like, “Could I be wrong?”, or “How
would I know if I were wrong?” Hint: it’s not the believers.

No, it’s Illing who’s the arrogant one, for he presumes that he, who
sits proudly at the Big People’s Table and can dispense with the need
for religion, must preach to all of us that those Little People at the
Children’s Table must have their pabulum faith—or a
substitute for it. It is he who doubts the ability of people to live
without convenient fictions. I have more faith in humanity than that,
and I use the word “faith” as a metaphor.

The pair recently engaged in an email exchange
on the ethical importance of intentions – and while Harris agrees it
was a disaster, he’s not sure it was actually a debate instead of a
conversation.

“They’re
superficially similar when the parties disagree, but to have one’s mind
changed in a debate is to lose the debate and very likely to lose face
before one’s audience,” Harris said. “Now this is an incredibly
counterproductive way to frame any inquiry into what is true.”

Harris published the exchange, which he had hoped would be “a civil
conversation on an important topic with a very influential thinker,” as a
way to salvage something of value from what turned out to be “a truly
pointless exercise.”

He said Chomsky’s supporters accused him of trying to “steal some
measure of his fame” and immediately found himself out of his depth when
the famed linguist “devastated (him) with the evidence of my own
intellectual misconduct and my ignorance of history and my blind faith
in the goodness of the U.S. government.”

The neuroscientist said he was “flabbergasted” by that response.

“Anyone who thinks I lost a debate here just doesn’t understand what I was trying to do,” he said.

Harris said he had hoped to learn what Chomsky actually believes
about the ethics of intent, and he hoped his own arguments would steer
leftists away from their “masochistic” tendencies.

He said Chomsky’s followers believe the U.S. was morally worse than
ISIS because it had, through “selfishness and ineptitude,” created ISIS
and victimized millions of people in other nations.

“This kind of masochism and misreading of both ourselves and of our
enemies has become a kind of religious precept on the left,” Harris
said. “I don’t think an inability to distinguish George Bush or Bill
Clinton from Saddam Hussein or Hitler is philosophically or politically
interesting, much less wise.”

He said most people who hold this “morally confused” view “Chomsky as their patriarch, and I suspect that’s not an accident.”

Harris complained that he encountered “contempt and false accusation
and highly moralizing language” throughout his exchange with Chomsky –
and he now wishes he had addressed those points immediately and
directly.

“Highly moralizing accusations work for people who think they are
watching a debate,” Harris said. “They convince most of the audience
that where there is smoke there must be fire. For instance, when Ben
Affleck called me and Bill Maher racist, that was all he had to do to
convince 50 percent of the audience.”

Harris said he’s never approached debates like a “high school
exercise,” where he remains committed to his point of view, because he
doesn’t “want to be wrong for a moment longer than I need to be.”

“I wanted to talk to him to see if there was some way to build a
bridge off of this island of masochism so that these sorts of people
that I’ve been hearing from for years could cross over to something more
reasonable, and it didn’t work out,” he said. “The conversation, as I
said, was a total failure, but I thought it was an instructive one.”

Background

Radiation is all around us. It is naturally present in our
environment and has been since the birth of this planet.

Consequently,
life has evolved in an environment which has significant levels of
ionizing radiation. It comes from outer space (cosmic), the ground
(terrestrial), and even from within our own bodies. It is present in the
air we breathe, the food we eat, the water we drink, and in the
construction materials used to build our homes. Certain foods such as
bananas and brazil nuts naturally contain higher levels of radiation
than other foods. Brick and stone homes have higher natural radiation
levels than homes made of other building materials such as wood. Our
nation's Capitol, which is largely constructed of granite, contains
higher levels of natural radiation than most homes.

Levels of natural or background radiation can vary greatly from one
location to the next. For example, people residing in Colorado are
exposed to more natural radiation than residents of the east or west
coast because Colorado has more cosmic radiation at a higher altitude
and more terrestrial radiation from soils enriched in naturally
occurring uranium. Furthermore, a lot of our natural exposure is due to
radon, a gas from the earth's crust that is present in the air we
breathe.

About half of the total annual average U.S. individual's radiation
exposure comes from natural sources. The other half is mostly from
diagnostic medical procedures. The average annual radiation exposure
from natural sources is about 310 millirem (3.1 millisieverts or mSv).
Radon and thoron gases account for two-thirds of this exposure, while
cosmic, terrestrial, and internal radiation account for the remainder.
No adverse health effects have been discerned from doses arising from
these levels of natural radiation exposure.

Man-made sources of radiation from medical, commercial, and
industrial activities contribute about another 310 mrem to our annual
radiation exposure. One of the largest of these sources of exposure is
computed tomography (CT) scans, which account for about 150 mrem. Other
medical procedures together account for about another 150 mrem each
year. In addition, some consumer products such as tobacco, fertilizer,
welding rods, exit signs, luminous watch dials, and smoke detectors
contribute about another 10 mrem to our annual radiation exposure.

The pie chart on the following page shows a breakdown of radiation
sources that contribute to the average annual U.S. radiation dose of 620
mrem. Nearly three-fourths of this dose is split between radon/thoron
gas and diagnostic medical procedures. Although there is a distinction
between natural and man-made radiation, they both affect us in the same
way.

Above
background levels of radiation exposure, the NRC requires that its
licensees limit maximum radiation exposure to individual members of the
public to 100 mrem (1mSv) per year, and limit occupational radiation
exposure to adults working with radioactive material to 5,000 mrem (50
mSv) per year. NRC regulations and radiation exposure limits are
contained in Title 10 of the Code of Federal Regulations, Part 20

Biological Effects of Radiation

We tend to think of biological effects of radiation in terms of their
effect on living cells. For low levels of radiation exposure, the
biological effects are so small they may not be detected. The body has
repair mechanisms against damage induced by radiation as well as by
chemical carcinogens. Consequently, biological effects of radiation on
living cells may result in three outcomes: (1) injured or damaged cells
repair themselves, resulting in no residual damage; (2) cells die, much
like millions of body cells do every day, being replaced through normal
biological processes; or (3) cells incorrectly repair themselves
resulting in a biophysical change.

The associations between radiation exposure and the development of
cancer are mostly based on populations exposed to relatively high levels
of ionizing radiation (e.g., Japanese atomic bomb survivors, and
recipients of selected diagnostic or therapeutic medical procedures).
Cancers associated with high-dose exposure (greater than 50,000 mrem)
include leukemia, breast, bladder, colon, liver, lung, esophagus,
ovarian, multiple myeloma, and stomach cancers. Department of Health and
Human Services literature also suggests a possible association between
ionizing radiation exposure and prostate, nasal cavity/sinuses,
pharyngeal and laryngeal, and pancreatic cancer.

The period of time between radiation exposure and the detection of
cancer is known as the latent period and can be many years. Those
cancers that may develop as a result of radiation exposure are
indistinguishable from those that occur naturally or as a result of
exposure to other carcinogens. Furthermore, National Cancer Institute
literature indicates that other chemical and physical hazards and
lifestyle factors (e.g., smoking, alcohol consumption, and diet)
contribute significantly to many of these same diseases.

Although radiation may cause cancers at high doses and high dose
rates, currently there are no data to establish unequivocally the
occurrence of cancer following exposure to low doses and dose rates –
below about 10,000 mrem (100 mSv).

Even so, the radiation protection community conservatively assumes
that any amount of radiation may pose some risk for causing cancer and
hereditary effect, and that the risk is higher for higher radiation
exposures. A linear, no-threshold (LNT) dose response relationship is
used to describe the relationship between radiation dose and the
occurrence of cancer. This dose-response hypothesis suggests that any
increase in dose, no matter how small, results in an incremental
increase in risk. The LNT hypothesis is accepted by the NRC as a
conservative model for determining radiation dose standards, recognizing
that the model may over estimate radiation risk.

High radiation doses tend to kill cells, while low doses tend to
damage or alter the genetic code (DNA) of irradiated cells. High doses
can kill so many cells that tissues and organs are damaged immediately.
This in turn may cause a rapid body response often called Acute
Radiation Syndrome. The higher the radiation dose, the sooner the
effects of radiation will appear, and the higher the probability of
death. This syndrome was observed in many atomic bomb survivors in 1945
and emergency workers responding to the 1986 Chernobyl nuclear power
plant accident.
Approximately 134 plant workers and firefighters
battling the fire at the Chernobyl power plant received high radiation
doses – 80,000 to 1,600,000 mrem (800 to 16,000 mSv) – and suffered from
acute radiation sickness. Of these, 28 died within the first three
months from their radiation injuries. Two more patients died during the
first days as a result of combined injuries from the fire and radiation.

Because radiation affects different people in different ways, it is
not possible to indicate what dose is needed to be fatal. However, it is
believed that 50% of a population would die within thirty days after
receiving a dose of between 350,000 to 500,000 mrem (3500 to 5000 mSv)
to the whole body, over a period ranging from a few minutes to a few
hours. This would vary depending on the health of the individuals before
the exposure and the medical care received after the exposure. These
doses expose the whole body to radiation in a very short period of time
(minutes to hours). Similar exposure of only parts of the body will
likely lead to more localized effects, such as skin burns.

Conversely, low doses – less than 10,000 mrem (100 mSv) – spread out
over long periods of time (years) don't cause an immediate problem to
any body organ. The effects of low doses of radiation, if any, would
occur at the cell level, and thus changes may not be observed for many
years (usually 5-20 years) after exposure.

Genetic effects and the development of cancer are the primary health
concerns attributed to radiation exposure. The likelihood of cancer
occurring after radiation exposure is about five times greater than a
genetic effect (e.g., increased still births, congenital abnormalities,
infant mortality, childhood mortality, and decreased birth weight).
Genetic effects are the result of a mutation produced in the
reproductive cells of an exposed individual that are passed on to their
offspring. These effects may appear in the exposed person's direct
offspring, or may appear several generations later, depending on whether
the altered genes are dominant or recessive.

Although radiation-induced genetic effects have been observed in
laboratory animals (given very high doses of radiation), no evidence of
genetic effects has been observed among the children born to atomic bomb
survivors from Hiroshima and Nagasaki.

NRC regulations strictly limit the amount of radiation that can be
emitted by a nuclear facility, such as a nuclear power plant. A 1991
study by the National Cancer Institute, "Cancer in Populations Living
Near Nuclear Facilities," concluded that there was no increased risk of
death from cancer for people living in counties adjacent to U.S. nuclear
facilities. At the NRC's request, the National Academy of Sciences is
currently engaged in a state-of-the-art update to the earlier study. The
new study will examine cancer rates in communities around operating and
decommissioned nuclear power plants, as well as nuclear fuel cycle
facilities.

Cancer risk: The study found that there is no excess cancer risk to
people living in the area of high natural background radiation in
Kerala.

Now it is official. In the January
2009 issue of the Health Physics Journal, researchers from the Regional
Cancer Centre (RCC), Thiruvananthapuram, and their collaborators have
shown that there is no excess cancer risk to people living in the area
of high natural background radiation in Kerala from exposure to
terrestrial gamma radiation.

The Journal highlighted the importance of the paper by carrying a photo of the beaches in its cover page.

Gamma radiation

The coastal belt of Karunagappally, Kerala, is known for high background radiation (HBR) from thorium-containing monazite sand.

In
the coastal panchayats, the median outdoor gamma radiation levels are
more than 4 mGy y{+-}{+1} and in certain locations, the levels are as
high as 70mGy y {+-}{+1}.(Gy is a unit of radiation dose; mGy is one
thousandth of a Gy; the annual gamma radiation level in normal locations
is on an average one mGy).

Based
on radiation level measurements, by a method perfected by scientists of
the Bhabha Atomic Research Centre, they chose a radiation sub cohort
consisting of 173,067 residents and analysed the cancer incidence in the
sub cohort, aged 30 to 84y (N=69958 followed up for 10.5 years).

They
estimated the cumulative radiation dose to each individual in the age
group based on the radiation doses received indoors and outdoors and
taking into account how long and where they stayed during the period.

By the end of 2005, they identified 1379 cases of cancer including 30 cases of leukaemia.

The results

Statistical analysis of the data showed no excess cancer risk from exposure to terrestrial gamma radiation.

In
site-specific analysis, they did not find any cancer site or leukaemia
to be significantly related to cumulative radiation dose.

“Although the statistical power of the study might not be adequate due
to the low dose, our cancer incidence study, together with previously
reported cancer mortality studies in the HBR area of Yangjiang, China
suggests it is unlikely that estimates of risk at low doses are
substantially greater than currently believed,” the researchers
concluded.

It appears that the researchers were in a
hurry to publish the paper. They did not use the complete data but
selected four coastal panchayats (Chavara, Neendakara, Panmana and
Alappad) which had HBR and two control areas (Oachira and Thevalakkara)
which have relatively low natural radiation levels.

They
estimated the excess risk as -0.13 Gy{+-}{+1} (95 per cent confidence
limit:-0.58, 0.46). The authors pointed out that the upper limit of 95
per cent confidence limit was lower than 0.97, which other researchers
got for pooled analysis for nuclear workers from 15 countries (BMJ,
2005) and slightly lower than 0.47 Gy{+-}{+1} reported in the study of
atomic bomb survivors in Hiroshima and Nagasaki (Radiation Research,
2007)

Authors highlighted some unique features of
their data. Unlike the nuclear workers study, RCC study included smoking
habits, an important contributing factor. The estimate of atomic bomb
survivors is a sex-averaged estimate for solid cancer unlike the RCC
study. The currently accepted radiation risk estimate is mostly based on
atomic bomb survivor study.

Regrettably, the
researchers did not estimate the substantial contribution of airborne
radon and thoron daughters to the individual radiation dose. This may
not affect the main conclusion that there is no excess cancer in areas
of high natural background radiation.

The limitations

Though
the analysis limited to six panchayats cannot be faulted
scientifically, they should use complete data including internal dose
from all panchayats for a reanalysis to do justice to the project and to
examine whether precise radiation risk estimate can be arrived at from
this study

Highlighting the negative radiation risk
coefficient of -0.13 Gy{+-}{+1}, proponents of those who believe in the
beneficial effects of radiation (hormesis theory) may argue that low
level radiation is helping to lower cancer risks!

They may not agree that lack of statistical power may be the reason for the negative result.

Breeder reactors could, in principle, extract almost all of the energy contained in uranium or thorium, decreasing fuel requirements by a factor of 100 compared to widely-used once-through light water reactors, which extract less than 1% of the energy in the uranium mined from the earth.[8] The high fuel efficiency of breeder reactors could greatly reduce concerns about fuel supply or energy used in mining. Adherents claim that with seawater uranium extraction, there would be enough fuel for breeder reactors to satisfy our energy needs for 5 billion years at 1983's total energy consumption rate, thus making nuclear energy effectively a renewable energy.[9][10]

Nuclear waste became a greater concern by the 1990s. In broad terms, spent nuclear fuel has two main components. The first consists of fission products, the leftover fragments of fuel atoms after they have been split to release energy. Fission products come in dozens of elements and hundreds of isotopes, all of them lighter than uranium. The second main component of spent fuel is transuranics (atoms heavier than uranium), which are generated from uranium or heavier atoms in the fuel when they absorb neutrons but do not undergo fission. All transuranic isotopes fall within the actinide series on the periodic table, and so they are frequently referred to as the actinides.

The physical behavior of the fission products is markedly different from that of the transuranics. In particular, fission products do not themselves undergo fission, and therefore cannot be used for nuclear weapons. Furthermore, only seven long-lived fission product isotopes have half-lives longer than a hundred years, which makes their geological storage or disposal less problematic than for transuranic materials.[11]

With increased concerns about nuclear waste, breeding fuel cycles became interesting again because they can reduce actinide wastes, particularly plutonium and minor actinides.[12] Breeder reactors are designed to fission the actinide wastes as fuel, and thus convert them to more fission products.

After "spent nuclear fuel" is removed from a light water reactor, it undergoes a complex decay profile as each nuclide decays at a different rate. Due to a physical oddity referenced below, there is a large gap in the decay half-lives of fission products compared to transuranic isotopes. If the transuranics are left in the spent fuel, after 1,000 to 100,000 years, the slow decay of these transuranics would generate most of the radioactivity in that spent fuel. Thus, removing the transuranics from the waste eliminates much of the long-term radioactivity of spent nuclear fuel.[13]

Today's commercial light water reactors do breed some new fissile material, mostly in the form of plutonium. Because commercial reactors were never designed as breeders, they do not convert enough uranium-238 into plutonium to replace the uranium-235 consumed. Nonetheless, at least one-third of the power produced by commercial nuclear reactors comes from fission of plutonium generated within the fuel.[14] Even with this level of plutonium consumption, light water reactors consume only part of the plutonium and minor actinides they produce, and nonfissile isotopes of plutonium build up, along with significant quantities of other minor actinides.[15] Even with reprocessing, reactor-grade plutonium is normally recycled only once in LWRs as mixed oxide fuel, with limited reductions in long-term waste radioactivity.[citation needed]

One measure of a reactor's performance is the "conversion ratio" (the average number of new fissile atoms created per fission event). All proposed nuclear reactors except specially designed and operated actinide burners[16] experience some degree of conversion. As long as there is any amount of a fertile material within the neutron flux of the reactor, some new fissile material is always created.

The ratio of new fissile material in spent fuel to fissile material consumed from the fresh fuel is known as the "conversion ratio" or "breeding ratio" of a reactor.

For example, commonly used light water reactors have a conversion ratio of approximately 0.6. Pressurized heavy water reactors (PHWR) running on natural uranium have a conversion ratio of 0.8.[17] In a breeder reactor, the conversion ratio is higher than 1. "Breakeven" is achieved when the conversion ratio becomes 1: the reactor produces as much fissile material as it uses.

"Doubling time" is the amount of time it would take for a breeder reactor to produce enough new fissile material to create a starting fuel load for another nuclear reactor. This was considered an important measure of breeder performance in early years, when uranium was thought to be scarce. However, since uranium is more abundant than thought, and given the amount of plutonium available in spent reactor fuel, doubling time has become a less important metric in modern breeder reactor design.[18][19]

"Burnup" is a measure of how much energy has been extracted from a given mass of heavy metal in fuel, often expressed (for power reactors) in terms of gigawatt-days per ton of heavy metal. Burnup is an important factor in determining the types and abundances of isotopes produced by a fission reactor. Breeder reactors, by design, have extremely high burnup compared to a conventional reactor, as breeder reactors produce much more of their waste in the form of fission products, while most or all of the actinides are meant to be fissioned and destroyed.[20]

In the past breeder reactor development focused on reactors with low breeding ratios, from 1.01 for the Shippingport Reactor[21][22] running on thorium fuel and cooled by conventional light water to over 1.2 for the Russian BN-350 liquid-metal-cooled reactor.[23] Theoretical models of breeders with liquid sodium coolant flowing through tubes inside fuel elements ("tube-in-shell" construction) suggest breeding ratios of at least 1.8 are possible.[24]

Types of breeder reactor

Production of heavy transuranic actinides in current thermal-neutron fission reactors through neutron capture and decays. Starting at Uranium-238, isotopes of Plutonium, Americium, and Curium are all produced. In a Fast Neutron Breeder Reactor, all these isotopes may be burned as fuel.

Many types of breeder reactor are possible:

A 'breeder' is simply a reactor designed for very high neutron economy with an associated conversion rate higher than 1.0. In principle, almost any reactor design could possibly be tweaked to become a breeder. An example of this process is the evolution of the Light Water Reactor, a very heavily moderated thermal design, into the Super Fast Reactor [25] concept, using light water in an extremely low-density supercritical form to increase the neutron economy high enough to allow breeding.

Aside from water cooled, there are many other types of breeder reactor currently envisioned as possible. These include molten-salt cooled, gas cooled, and liquid metal cooled designs in many variations. Almost any of these basic design types may be fueled by uranium, plutonium, many minor actinides, or thorium, and they may be designed for many different goals, such as creating more fissile fuel, long-term steady-state operation, or active burning of nuclear wastes.

For convenience, it is perhaps simplest to divide the extant reactor designs into two broad categories based upon their neutron spectrum, which has the natural effect of dividing the reactor designs into those which are designed to utilize primarily uranium and transuranics, and those designed to use thorium and avoid transuranics.

Fast breeder reactor or FBR uses fast (unmoderated) neutrons to breed fissile plutonium and possibly higher transuranics from fertile uranium-238. The fast spectrum is flexible enough that it can also breed fissile uranium-233 from thorium, if desired.

Thermal breeder reactor use thermal spectrum (moderated) neutrons to breed fissile uranium-233 from thorium (thorium fuel cycle). Due to the behavior of the various nuclear fuels, a thermal breeder is thought commercially feasible only with thorium fuel, which avoids the buildup of the heavier transuranics.

Reprocessing

Fission of the nuclear fuel in any reactor produces neutron-absorbing fission products. Because of this unavoidable physical process, it is necessary to reprocess the fertile material from a breeder reactor to remove those neutron poisons. This step is required if one is to fully utilize the ability to breed as much or more fuel than is consumed. All reprocessing can present a proliferation concern, since it extracts weapons usable material from spent fuel.[26] The most common reprocessing technique, PUREX, presents a particular concern, since it was expressly designed to separate pure plutonium. Early proposals for the breeder reactor fuel cycle posed an even greater proliferation concern because they would use PUREX to separate plutonium in a highly attractive isotopic form for use in nuclear weapons.[27][28]

Several countries are developing reprocessing methods that do not separate the plutonium from the other actinides. For instance, the non-water based pyrometallurgicalelectrowinning process, when used to reprocess fuel from an integral fast reactor, leaves large amounts of radioactive actinides in the reactor fuel.[8] More conventional advanced reprocessing systems which are based on water, like PUREX, include SANEX, UNEX, DIAMEX, COEX, and TRUEX, as well as proposals to combine PUREX with co-processes. All of these systems have better proliferation resistance than PUREX, although their adoption rate is low.[29][30]

In the thorium cycle, thorium-232 breeds by converting first to protactinium-233, which then decays to uranium-233. If the protactinium remains in the reactor, small amounts of U-232 are also produced, which has the strong gamma emitter Tl-208 in its decay chain. Similar to uranium-fueled designs, the longer the fuel and fertile material remain in the reactor, the more of these undesirable elements build up. Inside the envisioned commercial thorium reactors high levels of U232 would be allowed to accumulate, leading to extremely high gamma radiation doses from any uranium derived from thorium. These gamma rays complicate the safe handling of a weapon and the design of its electronics; this explains why U-233 has never been pursued for weapons beyond proof-of-concept demonstrations.[31]

Nuclear waste became a greater concern by the 1990s. Breeding fuel cycles attracted renewed interest because of their potential to reduce actinide wastes, particularly plutonium and minor actinides.[12] Since breeder reactors on a closed fuel cycle would use nearly all of the actinides fed into them as fuel, their fuel requirements would be reduced by a factor of about 100. The volume of waste they generate would be reduced by a factor of about 100 as well. While there is a huge reduction in the volume of waste from a breeder reactor, the activity of the waste is about the same as that produced by a light water reactor[citation needed].

In addition, the waste from a breeder reactor has a different decay behavior, because it is made up of different materials. Breeder reactor waste is mostly fission products, while light water reactor waste has a large quantity of transuranics. After spent nuclear fuel has been removed from a light water reactor for longer than 100,000 years, these transuranics would be the main source of radioactivity. Eliminating them would eliminate much of the long-term radioactivity from the spent fuel.[13]

In principle, breeder fuel cycles can recycle and consume all actinides,[9] leaving only fission products. As the graphic in this section indicates, fission products have a peculiar 'gap' in their aggregate half-lives, such that no fission products have a half-life longer than 91 years and shorter than two hundred thousand years. As a result of this physical oddity, after several hundred years in storage, the activity of the radioactive waste from a Fast Breeder Reactor would quickly drop to the low level of the long-lived fission products. However, to obtain this benefit requires the highly efficient separation of transuranics from spent fuel. If the fuel reprocessing methods used leave a large fraction of the transuranics in the final waste stream, this advantage would be greatly reduced.[8]

The thorium fuel cycle inherently produces lower levels of heavy actinides. The fertile material in the thorium fuel cycle has an atomic weight of 232, while the fertile material in the uranium fuel cycle has an atomic weight of 238. That mass difference means that thorium-232 requires six more neutron capture events per nucleus before the transuranic elements can be produced. In addition to this simple mass difference, the reactor gets two chances to fission the nuclei as the mass increases: First as the effective fuel nuclei U233, and as it absorbs two more neutrons, again as the fuel nuclei U235.[38][39]

A reactor whose main purpose is to destroy actinides, rather than increasing fissile fuel stocks, is sometimes known as a burner reactor. Both breeding and burning depend on good neutron economy, and many designs can do either. Breeding designs surround the core by a breeding blanket of fertile material. Waste burners surround the core with non-fertile wastes to be destroyed. Some designs add neutron reflectors or absorbers.[16]

Breeder reactor concepts

There are several concepts for breeder reactors; the two main ones are:

Reactors with a fast neutron spectrum are called fast breeder reactors (FBR) – these typically utilize uranium-238 as fuel.

Reactors with a thermal neutron spectrum are called thermal breeder reactors – these typically utilize thorium-232 as fuel.

Fast breeder reactor

Schematic diagram showing the difference between the Loop and Pool types of LMFBR.

Pool type, in which the primary heat exchangers and pumps are immersed in the reactor tank

All current fast neutron reactor designs use liquid metal as the primary coolant, to transfer heat from the core to steam used to power the electricity generating turbines. FBRs have been built cooled by liquid metals other than sodium—some early FBRs used mercury, other experimental reactors have used a sodium-potassiumalloy called NaK. Both have the advantage that they are liquids at room temperature, which is convenient for experimental rigs but less important for pilot or full scale power stations. Lead and lead-bismuth alloy have also been used. The relative merits of lead vs sodium are discussed here. Looking further ahead, four of the proposed generation IV reactor types are FBRs:[40]

In many designs, the core is surrounded in a blanket of tubes containing non-fissile uranium-238 which, by capturing fast neutrons from the reaction in the core, is converted to fissile plutonium-239 (as is some of the uranium in the core), which is then reprocessed and used as nuclear fuel. Other FBR designs rely on the geometry of the fuel itself (which also contains uranium-238), arranged to attain sufficient fast neutron capture. The plutonium-239 (or the fissile uranium-235) fission cross-section is much smaller in a fast spectrum than in a thermal spectrum, as is the ratio between the 239Pu/235U fission cross-section and the 238U absorption cross-section. This increases the concentration of 239Pu/235U needed to sustain a chain reaction, as well as the ratio of breeding to fission.[16]

On the other hand, a fast reactor needs no moderator to slow down the neutrons at all, taking advantage of the fast neutrons producing a greater number of neutrons per fission than slow neutrons. For this reason ordinary liquid water, being a moderator as well as a neutron absorber, is an undesirable primary coolant for fast reactors. Because large amounts of water in the core are required to cool the reactor, the yield of neutrons and therefore breeding of 239Pu are strongly affected. Theoretical work has been done on reduced moderation water reactors, which may have a sufficiently fast spectrum to provide a breeding ratio slightly over 1. This would likely result in an unacceptable power derating and high costs in an liquid-water-cooled reactor, but the supercritical water coolant of the SCWR has sufficient heat capacity to allow adequate cooling with less water, making a fast-spectrum water-cooled reactor a practical possibility.[25]

Integral fast reactor

One design of fast neutron reactor, specifically designed to address the waste disposal and plutonium issues, was the integral fast reactor (also known as an integral fast breeder reactor, although the original reactor was designed to not breed a net surplus of fissile material).[41][42]

To solve the waste disposal problem, the IFR had an on-site electrowinning fuel reprocessing unit that recycled the uranium and all the transuranics (not just plutonium) via electroplating, leaving just short half-lifefission products in the waste. Some of these fission products could later be separated for industrial or medical uses and the rest sent to a waste repository (where they would not have to be stored for anywhere near as long as wastes containing long half-life transuranics). The IFR pyroprocessing system uses molten cadmium cathodes and electrorefiners to reprocess metallic fuel directly on-site at the reactor.[43] Such systems not only commingle all the minor actinides with both uranium and plutonium, they are compact and self-contained, so that no plutonium-containing material ever needs to be transported away from the site of the breeder reactor. Breeder reactors incorporating such technology would most likely be designed with breeding ratios very close to 1.00, so that after an initial loading of enriched uranium and/or plutonium fuel, the reactor would then be refueled only with small deliveries of natural uranium metal. A quantity of natural uranium metal equivalent to a block about the size of a milk crate delivered once per month would be all the fuel such a 1 gigawatt reactor would need.[44] Such self-contained breeders are currently envisioned as the final self-contained and self-supporting ultimate goal of nuclear reactor designers.[8][16] The project was canceled in 1994 by United States Secretary of EnergyHazel O'Leary.[45][46]

Other fast reactors

The graphite core of the Molten Salt Reactor Experiment

Another proposed fast reactor is a fast molten salt reactor, in which the molten salt's moderating properties are insignificant. This is typically achieved by replacing the light metal fluorides (e.g. LiF, BeF2) in the salt carrier with heavier metal chlorides (e.g., KCl, RbCl, ZrCl4).

Several prototype FBRs have been built, ranging in electrical output from a few light bulbs' equivalent (EBR-I, 1951) to over 1,000 MWe. As of 2006, the technology is not economically competitive to thermal reactor technology—but India, Japan, China, South Korea and Russia are all committing substantial research funds to further development of Fast Breeder reactors, anticipating that rising uranium prices will change this in the long term. Germany, in contrast, abandoned the technology due to safety concerns. The SNR-300 fast breeder reactor was finished after 19 years despite cost overruns summing up to a total of 3.6 billion Euros, only to then be abandoned.[47]

As well as their thermal breeder program, India is also developing FBR technology, using both uranium and thorium feedstocks.

Thermal breeder reactor

The Shippingport Reactor, used as a prototype Light Water Breeder for five years beginning in August, 1977

The advanced heavy water reactor (AHWR) is one of the few proposed large-scale uses of thorium.[48] India is developing this technology, their interest motivated by substantial thorium reserves; almost a third of the world's thorium reserves are in India, which also lacks significant uranium reserves.

The third and final core of the Shippingport Atomic Power Station 60 MWe reactor was a light water thorium breeder, which began operating in 1977.[49] It used pellets made of thorium dioxide and uranium-233 oxide; initially, the U-233 content of the pellets was 5-6% in the seed region, 1.5-3% in the blanket region and none in the reflector region. It operated at 236 MWt, generating 60 MWe and ultimately produced over 2.1 billion kilowatt hours of electricity. After five years, the core was removed and found to contain nearly 1.4% more fissile material than when it was installed, demonstrating that breeding from thorium had occurred.[50][51]

The liquid fluoride thorium reactor (LFTR) is also planned as a thorium thermal breeder. Liquid-fluoride reactors may have attractive features, such as inherent safety, no need to manufacture fuel rods and possibly simpler reprocessing of the liquid fuel. This concept was first investigated at the Oak Ridge National LaboratoryMolten-Salt Reactor Experiment in the 1960s. From 2012 it became the subject of renewed interest worldwide.[52] Japan, China, the UK, as well as private US, Czech and Australian companies have expressed intent to develop and commercialize the technology.

Breeder reactor controversy

Like many aspects of nuclear power, fast breeder reactors have been subject to much controversy over the years. In 2010 the International Panel on Fissile Materials said "After six decades and the expenditure of the equivalent of tens of billions of dollars, the promise of breeder reactors remains largely unfulfilled and efforts to commercialize them have been steadily cut back in most countries". In Germany, the United Kingdom, and the United States, breeder reactor development programs have been abandoned.[53][54] The rationale for pursuing breeder reactors—sometimes explicit and sometimes implicit—was based on the following key assumptions:[54][55]

It was expected that uranium would be scarce and high-grade deposits would quickly become depleted if fission power were deployed on a large scale; the reality, however, is that since the end of the cold war, uranium has been much cheaper and more abundant than early designers expected.[56]

It was expected that breeder reactors would quickly become economically competitive with the light-water reactors that dominate nuclear power today, but the reality is that capital costs are at least 25% more than water cooled reactors.

It was thought that Breeder reactors could be as safe and reliable as light-water reactors, but safety issues are cited as a concern with fast reactors that use a sodium coolant, where a leak could lead to a sodium fire.

It was expected that the proliferation risks posed by breeders and their “closed” fuel cycle, in which plutonium would be recycled, could be managed. But since plutonium breeding reactors produce plutonium from U238, and thorium reactors produce fissile U233 from thorium, all breeding cycles could theoretically pose proliferation risks.[57]

These problems have stymied their deployment and lent credence to calls for their abandonment.

There are some past anti-nuclear advocates that have become pro-nuclear power as a clean source of electricity since breeder reactors effectively recycle most of their waste. This solves one of the most important negative issues of nuclear power. In the documentary "Pandora's Promise", a case is made for breeder reactors because they provide a real, high kW alternative to fossil fuel energy. According to the movie, one pound of uranium provides as much power as 5000 barrels of oil.[58]

FBRs have been built and operated in the United States, the United Kingdom, France, the former USSR, India and Japan.[1] An experimental FBR in Germany was built but never operated. As of 2014 one such reactor was being used for power generation, with another scheduled for early 2015. Several reactors are planned, many for research related to the Generation IV reactor initiative.[citation needed]

The Soviet Union (comprising Russia and other countries, dissolved in 1991) constructed a series of fast reactors, the first being mercury-cooled and fueled with plutonium metal, and the later plants sodium-cooled and fueled with plutonium oxide.

BR-1 (1955) was 100W (thermal) was followed by BR-2 at 100 kW and then the 5MW BR-5.

BOR-60 (first criticality 1969) was 60 MW, with construction started in 1965.[62]

Future plants

In 2012 an FBR called the Prototype Fast Breeder Reactor was under construction in India, due to be completed that year, with commissioning date known by mid-year.[63][64] The FBR program of India includes the concept of using fertile thorium-232 to breed fissile uranium-233. India is also pursuing the thorium thermal breeder reactor. A thermal breeder is not possible with purely uranium/plutonium based technology. Thorium fuel is the strategic direction of the power program of India, owing to the nation's large reserves of thorium, but worldwide known reserves of thorium are also some four times those of uranium. India's Department of Atomic Energy (DAE) said in 2007 that it would simultaneously construct four more breeder reactors of 500 MWe each including two at Kalpakkam.[65]

China also initiated a research and development project in thorium molten-salt thermal breeder reactor technology (Liquid fluoride thorium reactor), formally announced at the Chinese Academy of Sciences (CAS) annual conference in January 2011. Its ultimate target is to investigate and develop a thorium-based molten salt nuclear system over about 20 years.[68][69]

Kirk Sorensen, former NASA scientist and Chief Nuclear Technologist at Teledyne Brown Engineering, has long been a promoter of thorium fuel cycle and particularly liquid fluoride thorium reactors. In 2011, Sorensen founded Flibe Energy, a company aimed to develop 20-50 MW LFTR reactor designs to power military bases.[70][71][72][73]South Korea is developing a design for a standardized modular FBR for export, to complement the standardized PWR (Pressurized Water Reactor) and CANDU designs they have already developed and built, but has not yet committed to building a prototype.

A cutaway model of the BN-600 reactor, superseded by the BN-800 reactor family.

Russia has a plan for increasing its fleet of fast breeder reactors significantly. A BN-800 reactor (800 MWe) at Beloyarsk was completed in 2012, succeeding a smaller BN-600. In June 2014 the BN-800 was started in the minimum power mode.[74] It is expected to start to work in nominal power mode later in 2015.[75]

Plans for the construction of an even larger BN-1200 reactor (1,200 MWe) initially anticipated completion in 2018, with two additional BN-1200 reactors built by the end of 2030.[76] However in 2015 Rosenergoatom postponed construction indefinitely to allow fuel design to be improved after more experience of operating the BN-800 reactor, and amongst cost concerns.[75]

An experimental lead-cooled fast reactor, BREST-300 will be built at the Siberian Chemical Combine (SCC) in Seversk. The BREST design is seen as a successor to the BN series and the 300 MWe unit at the SCC could be the forerunner to a 1,200 MWe version for wide deployment as a commercial power generation unit. The development program is as part of an Advanced Nuclear Technologies Federal Program 2010-2020 that seeks to exploit fast reactors as a way to be vastly more efficient in the use of uranium while 'burning' radioactive substances that otherwise would have to be disposed of as waste. BREST refers to bystry reaktor so svintsovym teplonositelem, Russian for 'fast reactor with lead coolant'. Its core would measure about 2.3 metres in diameter by 1.1 metres in height and contain 16 tonnes of fuel. The unit would be refuelled every year, with each fuel element spending five years in total within the core. Lead coolant temperature would be around 540 °C, giving a high efficiency of 43%, primary heat production of 700 MWt yielding electrical power of 300 MWe. The operational lifespan of the unit could be 60 years. The design is expected to be completed by NIKIET in 2014 for construction between 2016 and 2020.[77]

In September 2010 the French government allocated 651.6 millions euros to the Commissariat à l'énergie atomique to finalize the design of "Astrid" (Advanced Sodium Technological Reactor for Industrial Demonstration), a 600 MW reactor design of the 4th generation to be operational in 2020.[80][81]As of 2013 the UK had shown interest in the PRISM reactor and was working in concert with France to develop ASTRID.

The traveling wave reactor proposed in a patent by Intellectual Ventures is a fast breeder reactor designed to not need fuel reprocessing during the decades-long lifetime of the reactor. The breed-burn wave in the TWR design does not move from one end of the reactor to the other but gradually from the inside out. Moreover, as the fuel's composition changes through nuclear transmutation, fuel rods are continually reshuffled within the core to optimize the neutron flux and fuel usage at any given point in time. Thus, instead of letting the wave propagate through the fuel, the fuel itself is moved through a largely stationary burn wave. This is contrary to many media reports, which have popularized the concept as a candle-like reactor with a burn region that moves down a stick of fuel. By replacing a static core configuration with an actively managed "standing wave" or "soliton" core, TerraPower's design avoids the problem of cooling a highly variable burn region. Under this scenario, the reconfiguration of fuel rods is accomplished remotely by robotic devices; the containment vessel remains closed during the procedure, and there is no associated downtime.[84]

About Me

My formal training is in chemistry. I also read a great deal of physics and biology. In fact I very much enjoy reading in general, mostly science, but also some fiction and history. I also enjoy computer programming and writing. I like hiking and exploring nature. I also enjoy people; not too much in social settings, but one on one; also, people with interesting or "off-beat" minds draw me to them. I also have some interest in Buddhism.

These days I get a lot more information from the internet, primarily through Wiki. Some television, e. g., documentaries, PBS shows like "Nova" and "Nature".

My favorite science writers are Jacob Bronowski ("The Ascent of Man") and Richard Dawkins (his "The Blind Watchmaker" is right up there up Ascent). I also have a favorite writer on Buddhism, Pema Chodron. Favorite films are "Annie Hall" (by Woody Allen), "The Maltese Falcon", "One Flew Over The Cuckoo's Nest", "As Good As It Gets", "Conspiracy Theory", Monty Python's "Search For The Holy Grail" and "Life of Brian", and a few others which I can't think about at the moment.

I love a number of classical works (Beethoven's "Pastoral", "Afternoon Of A Fawn" and "Clair De Lune" by Debussey , Pachelbel's "Canon" come to mind. My favorite piece is probably Gershwin's "Rhapsody in Blue". But I also enjoy a great deal in modern music, including many jazz pieces, folk songs by people like Dylan, Simon and Garfunkel, a hodgepodge of pieces by Crosby, Stills, and Nash, Niel Young, and practically everything the Beatles wrote.

My life over the last few years has been in some disarray, but I am finally "getting it together.". As I am very much into the sciences and writing, I would like to move more in this direction. I also enjoy teaching. As for my political leanings, most people would probably describe as basically liberal, though not extremely so. My religious leanings are to the absolutely none: I've alluded to my interest in Buddhism, but again this is not any supernatural or scientifically untested aspect of it but in the way it provides a powerful philosophy and set of practical, day to day methods of dealing with myself and the other human beings.